Skyvan Glory (optical phenomenon)
Glory of a Skyvan and a RV-6 in the clouds over Galveston Texas, taken from the Skyvan while flying through the clouds.
The glory phenomenon involves refraction, reflection, and diffraction in which light is bent through 180° in a complex pattern. A portion of the light ultimately disperses from all edges of the drop in the constructive and destructive wave-interference pattern of diffraction, producing the rings. The effect is most often noticed surrounding the shadow of an airplane on a cloud bank below, like the Skyvan I was flying in as well as an RV-6 behind it.
Canadian Aviation Blog